1. Field of the Invention
The present invention relates to an ultrasonic transducer which is used in the body cavity and is preferable to ultrasonic diagnosis and the like.
2. Description of the Related Art
A mechanical scanning ultrasonic endoscope is used for the spectrographic diagnosis of the luminal surface organ and the ultrasonic diagnosis of the peripheral organ and the tissue by inserting a dedicated scope into the digestive tract such as the esophagus, the stomach, the duodenum, and the large intestine or the urinary tract such as the urethra, bladder, and the ureter. An ultrasonic transducer for transmitting and receiving ultrasonic waves is attached to the distal end portion of the mechanical scanning ultrasonic endoscope.
The ultrasonic transducer of the mechanical scanning ultrasonic endoscope is covered with an exterior cap containing a resin member for ultrasonic transmission. The exterior cap is filled with an acoustic medium. The acoustic medium efficiently propagates, through the living body, the ultrasonic waves generated by the ultrasonic transducer. The acoustic medium contains, as a general material, insulating oil such as liquid paraffin and butanediol.
However, the insulating oil has a high acoustic-attenuating rate. As a consequence, the ultrasonic endoscope with a high frequency capable of providing an image with a high resolution has such a problem that an ultrasonic signal is attenuated in the acoustic medium and thus a preferable image is not obtained.
In order to prevent the occurrence of the problem, the acoustic medium contains water that displays a low acoustic-attenuation, or an aqueous solution obtained by adding an additive to water (hereinafter, simply referred to as an aqueous solution).
The aqueous solution exposes the ultrasonic transducer for a long time and then the property of the ultrasonic transducer gradually deteriorates. Therefore, in order to prevent the deterioration in property of the ultrasonic transducer, the aqueous solution is injected every ultrasonic endoscope examination and the aqueous solution is removed after finishing the examination.
However, with the ultrasonic endoscope inserted into the body cavity, the injection and removal of the aqueous solution after/before the examination becomes a complicated work for an operator in view of the configuration of the ultrasonic endoscope.
Then, in the ultrasonic endoscope having the ultrasonic transducer with the high-frequency property, the ultrasonic transducer is subjected to thin-film coating (hereinafter, waterproof coating) using high water-resisting resin.